1. Field of the Invention
This invention relates to a display device that creates very high resolution real time images. Several subregions within individual pixels of a display are illuminated in rapid succession while changing the transparency of each pixel as necessary just prior to each illumination period, thus creating an image made of the illuminated subregions instead of the pixels themselves. More particularly, this invention relates to an optical and illumination system that can be used to accomplish such sub pixel illumination, especially in combination with a reflective integrated circuit ferroelectric liquid crystal display (ICFLCD) or other reflective light valve arrays such as a digital light processor (DLP) display.
2. Description of Related Art
U.S. Pat. No. 5,036,385 (Eichenlaub) discloses an optical and illumination system whereby subregions of a transmissive LCD may be illuminated in succession so as to produce an image made of the subregions instead of the pixels themselves. The produced image thus may have a much higher resolution than the LCD itself. Furthermore, U.S. Pat. No. 5,410,345 (Eichenlaub) discloses a detailed construction and operation of an illumination system and optics that may be used to illuminate several subregions of each pixel in succession. U.S. Pat. No. 5,428,366 (Eichenlaub) discloses an optical and illumination system that can create high resolution color images that do not display color breakup by illuminating subregions of pixels in succession. The aforementioned devices were designed primarily with a transmissive, direct view LCD as the light valve.
There are now available a new class of light valves that are designed primarily for head mounted and projection applications. These devices, though relying on different, specific optical technologies to operate, are reflective, are miniature devices (e.g., measuring less than 20 mm on a side and possess pixels that are less than 20 microns on a side), and possess extremely fast address and pixel response rates. There are also various monochrome devices, with color images typically being created by field sequential color illumination or by combining the images of three displays, each illuminated by a different color. Examples are ICFLCDs and other non-transmissive LCDs. However, the optical and illumination system of the aforementioned Eichenlaub patents are not readily adaptable to such newer classes of light valves since they are non-transmissive to light.
Simple mathematics tells one that the display of images with resolution matching the eye's limit and having a sufficiently wide field of view (FOV) for head mounted device (HMD) applications requires an extremely high resolution display. The eye can resolve to less than 1 minute of arc, depending on ambient light, color, and other factors. One minute of arc will be used for illustrative purposes. A device that is capable of displaying one minute resolution would be made up of red, green, and blue pixel triads that subtend no more than ½ minute of arc. A display with pixels subtending ½ minute of arc and covering 80 degrees horizontally (the minimum that is considered acceptable, with 180 degrees or more considered the optimum), and somewhat less vertically (this would be 60 degrees for a display with a typical width to height ratio) would have a total resolution of 9600 triads by 7200 triads. Clearly such a display is far beyond the current state-of-the-art. Approximately 2000×2000 resolution is the best that has been attained on real time displays. 1280×1024 resolution is the highest available in commercial virtual reality systems using miniature cathode ray tubes (CRTs). The resolution of the more compact and lighter weight LCD based systems is much lower. Thus a state-of-the-art virtual reality display possesses less than 1/50th the number of pixels required for the vision limited resolution display just described.
One company, LEEP Systems, currently makes optics that partially overcome this problem by distorting the display—keeping it compressed and thus providing high angular resolution in the center, while stretching it at the edges to provide as much of a peripheral view as possible. Software corrects for this distortion on the image itself, which is rendered as a fish eye image on the display and looks normal when viewed through the optics. Resolution at the center of the FOV is improved by a factor of three. Since the human visual system can perceive high resolution only near the gaze point, and since an observer typically spends most of the time looking straight ahead, this system provides some improvement over other devices.
Recently, it has been proposed to incorporate high resolution inserts spanning 5 to 30 degrees (the best size to be determined experimentally) within low resolution LCD images. The high resolution inserts, if small enough could approach the human eyes resolution limit. The proposed system requires four LCDs, and would be rather bulky, with the extra LCDs mounted above or to the side of the user's head. Moving inserts have been implemented in helmet displays, where two helmet displays provide movable high resolution inserts within low resolution images by means of eye trackers, movable mirrors, and two thick fiber optic cables extending to remote displays and optics. Thus, such approaches to achieve eye limited resolution in HMD systems require bulky, heavy equipment that involves high resolution inserts in lower resolution fields.
Accordingly, it is an object of this invention to provide an optical and illumination system that may be used to accomplish sub pixel illumination with a reflective ICFLCD or other reflective light valve, and especially, illumination of subpixel regions in rapid succession.
It is another object of this invention to provide a display device that creates very high resolution real time images, including higher resolution than obtainable with the devices described in the aforementioned Eichenlaub patents.
It is another object of this invention to provide an optical and illumination system that may be used to direct light efficiently from a reflective light valve to a projection lens, in the case of a projected image, or to an eyepiece, in the case of a head mounted system.
It is another object of this invention to provide a relatively light weight LCD-based display device which can produce very high resolution images across the entire field without inserts, cumbersome equipment, or eye trackers.
It is yet another object of this invention to provide displays and associated optics systems that are higher in resolution, yet lighter in weight than present CRT imaging systems and roughly the same size as present LCD based virtual reality (VR) displays.